Process of concentrating ores



' Patented July 5, 1938 PATENT OFFICE PROCESS OF CONCENTRATING ORES Anderson W. Ralston and William 0. Pool, Chicago, Ill., assignors to Armour and Company, Chicago, Ill., a corporation of Illinois No Drawing. Application May 11, 1937,

Serial No. 142,017

6 Claims. 209-166) This invention relates to processesof concentrating ores, and it comprises processes of concentrating ores by flotation methods, such as froth flotation, wherein an aqueous pulpof the d ore is separated into a concentrate high in mineral values in the presence of mixtures of alkali metal salts of straight-chain saturated and unsaturated aliphatic carboxylic acids containing at least three and not more than ten carbon atoms In and a mixture of straight-chain saturated and unsaturated aliphatic hydrocarbons having from five to fourteen'carbon atoms.

In our co-pending application Serial No. 141,874 filed May 10, 1937, we have described flotation agents comprising mixtures of saturated and I unsaturated aliphatic carboxylic acids containing from threeto ten carbon atoms and saturated and unsaturated aliphatic straight-chain hydrocarbons of low molecular weight containing from about five to fourteen carbon atoms. Said mixtures, when added to an aqueous ore pulp, will float the following minerals: Pyrolusite, malachite, chalcopyrite, chalcocite, galena, rutile, franklinite, apatite, ilmenite, zincite, magnetite, andpyrite when the amount of flotation agent is about 300 parts per million of aqueous ore pulp.-

We have now discovered that even better results are obtained when such flotation agent, namely a mixture of saturated and unsaturated carboxylic acids'and hydrocarbons, is added to the ore pulp and the aliphatic carboxylic acids therein converted to alkali metal salts prior to subjecting the ore pulp to-froth flotation. Consequently, in accordance with the present invention, the mineral values in the ore are separated from the 'gangue in the presence of straight-chain saturated and unsaturated hydrocarbons having from flve to fourteen carbon atoms and alkali metal salts of saturated and 40 unsaturated aliphatic carboxylic acids having from three to ten'ca'rbon atoms. Although the flotation agents of the aforesaid application are entirely suitable for most purposes, we find that in many cases better results are obtained when the carboxylic acids of said flotation agents are converted to alkali metal salts. Thus, for example, in addition to the res given above we can float; by processes of} he present invention, sphalerite, collophanite and magnetite. This Cir means that by the processes of the present in- 1 The flotation agents which we use in the present-s 2,033,536 and 2,033,537.

ent invention are best'prepared by hydrolyzing mixtures of nitriles and hydrocarbons obtained as a condensate when higher fatty acid nitriles, such as stearonitrile and lard fatty acid nitriles, are subjected to pyrolytic decomposition. The nitriles in such a mixture will contain from three to tencarbon atoms and, when hydrolyzed with caustic soda or potas um hydroxide, these ni triles are converted to alkali metal salts of the corresponding fatty acids. Proprionitrile yields, 10 on hydrolysis with caustic soda, the sodium salt of propionic acid and the other nitriles in the mixture are likewise converted to sodium or potassium salts of their carboxylic acid equivalents.

In order that our invention may be clearly understood we shall first briefly outline the preparation of such nitrile-hydrocarbon mixtures.

Methods of obtaining these are described and claimed in the Ralston, Pool and Harwood Pat- 0 These methods in general consist in subjecting high molecular weight nitriles, for example, stearonitrile, palmitonitrile, or large fatty acid nitriles to pyrolytic conditions resulting in the formation of a con- 0 densate containing lower molecular weight nitriles and aliphatic straight-chain hydrocarbons. The high molecular weight nitriles can be cracked in liquid phase or in vapor phase in the presence of a catalyst. When, for example, stearonitrile is subjected to liquid phase crack- 30 ing the condensed reaction product obtained is a pale yellow liquid comprising a mixture of saturated and unsaturated nitriles, together with saturated and unsaturated straight-chain hydrocarbons. This nitrile mixture can contain nitriles having from three to ten carbon atoms and hydrocarbons, both saturated and unsaturated, having from five to ten carbon atoms.

The entire mixture obtained as a condensate can then be directly hydrolyzed by admixing it 40 with caustic soda or caustic potash of about twenty percent concentration and heating the mixture in an autoclave or bomb until all the nitriles therein have been converted to sodium or potassium salts of the corresponding aliphatic acids. The hydrolyzate consists of an aqueous solution of the said salts admixed with the hydrocarbons. To the aqueous mixture we then add a mineral acid, such asjsulfuric or hydro 50 chloric, to decompose the aliphatic carboxylic acid salts thus liberating the corresponding free fatty acids which at once dissolve in the hydrocarbon portions of the mixture. The hydrocarbon solution of free carboxylic acids is then sepiication.

This hydrocarbon solution will on the averag contain about fifty percent saturated and unsaturated carboxylic acids, the reminder being saturated and unsaturated hydrocarbons having arated from the aqueous layer by simple stratifrom five to fourteen carbon atoms. The hydro- In other words, these acids extend from propionic to capric.

This mixture of carboxylic acids and hydrocarbons is then added to an aqueous pulp of the mineral to be concentrated in proportions of about 150 to 300 parts of the mixture to about one million parts of water. The carboxylic acids are next converted to their corresponding alkali metal salts, more usually the sodium salts, but we can convert them to potassium salts, by adding just enough caustic soda or caustic potash to neutralize the acids. We then: subject the ore pulp to froth flotation in the usual way and in accordance with accepted practise,- finally skimming off a goncentrate of the desired mineral value as a roth.

When hydrolyzlng the mixture of nitriles and hydrocarbons we can use varying amounts of caustic soda or caustic potash solution of from ten to twenty percent strength. Generally we admix about equal quantities of the nitrile-hydrocarbon mixture' and caustic soda of the said strength and heat the mixture in a bomb or autoclave to a temperature of about 200 C. to insure that all of the nitriles'are hydrolyzed to carboxylic acid salts.

The above description will indicate the general methods we employ for converting the nitrilehydrocarbon mixtures to hydrocarbon solutions of aliphatic carboxylic acids. There are numerous variations in the ultimate composition of the hydrocarbon solution of carboxylic acids possible.

The entire condensate obtained when the higher nitriles are cracked will contain saturated and unsaturated nitriles containing from three to ten carbon atoms. By prolonging the cracking, however, nitriles having from eight to ten carbon atoms are further decomposed into hydrocarbons and nitriles having less than eight carbon atoms. Consequently, the composition of the hydrocarbon solution of aliphatic carboxylic acids which we add to the ore pulp and then neutralize with alkali can be varied by variations in the extent to which the higher nitriles are cracked.

Or we can first condense a cracked condensate containing nitriles having three to ten carbon atoms and then fractionally distil such a mixture to obtain fractions in which nitriles of three, four and five carbon atoms predominate, or fractions in which four, five and six carbon atom nitriles predominate. For example, that fraction of nitriles and hydrocarbons boiling from 40 C. to 110 C. will consist mostly of capronitrile and its unsaturated analogues and low boiling hydrocarbons. hydrolysis, recover a hydrocarbon solution of the free aliphatic carboxylic acids, namely mostly pentanoic and pentenoic acids and hydrocarbons this mixture is hydrolyzed We can subject such a distillate to consisting mostly of pentane, p entene, hexane, hexene and heptane and heptene. When we add such a hydrocarbon solution to an aqueous pulp or slurry of any of the above-listed ores, neutralize the carboxylic acids with caustic soda,.'a'nd then aerate, we are subjecting such an ore to froth flotation in the presence of sodium salts of hexanoic and hexenoic acids and low boiling saturated and unsaturated straightchain hydrocarborg ca Or we n hydrolyze another fraction having a boilingv int range of about 110 C. to 175 C. Such a 'nitrile-hydrocarbon fraction will consist mostly of capronitrile and oenanthonitrile and their unsaturated analogues, together with saturated and unsaturated ydrocarbons. When e ultimately recover a hydrocarbon solutlonof hexanoic, hexenoic, heptanoic, and heptenoic acids, together with straight-chain saturated and unsaturated hydrocarbons, such as octane, octene, nonane, nonene ized with caustic soda, gives us a mixture of ore.

pulp containing sodium salts of hexanoic, hexenoic, heptanoic and heptenoic acids, and. the above-stated hydrocarbons.

In similar ways we can prepare hydrocarbon solutions containing any aliphatic acid, or any quantity thereof in which the aliphatic acid contains from three to ten carbon atoms.

In broad aspects then, our process comprises subjecting the mineral values in ores to concentration by flotation in the presence of small amounts of alkali metal salts of at least one unsaturated aliphatic carboxylic acid having from three to ten carbon atoms and aliphatic saturated and unsaturated straight-chain hydrocar- We believe that hydrocarbons which we add to the ore pulp have some specific action on the mineral values to be floated so that the surfaces of the mineral values become more readily wetted by water. The aliphatic carboxylic acid salts, in the presence of the hydrocarbons, appear to function.

bons having from five to fourteen carbon atoms.

other ways, add such a solution to the aqueous ore pulp, neutralize with caustic soda, and subject to froth flotation. Even number carbon atom chain carboxylic acids are not abundant in nature and those containing an odd number of carbon atoms, with the exception of valeric' acid, are extremely rare. Those containing one double bond do not occur naturally. The synthesis of this mixture would be very costly and diflicult and consequently, the cheapest source thereof is the product obtained from cracking higher molecular weight nitriles. We can, for example, separate the nitriles from the nitrile-hydrocarbon distillates obtained, fractionally distil the nitriles to obtain individual nitriles, and then convert these to the corresponding aliphatic carboxylic acid. Having isolated the separate acids we can then make up mixtures of straight-chain hydrocarbons of the class described and mixtures of one or more of the aliphatic carboxylic acids.

But for commercial purposes we find it best to directly hydrolyze a nitrile-hydrocarbon distillate containing nitriles corresponding to the carboxylic acids we wish to add to the ore pulp and convert to alkali metal salts.

Having thus described our invention, what we claim is:

1. The method of -froth concentrating ores which comprises admixing with an aqueous ore pulp a small amount of a mixture of straightchain saturated and unsaturated aliphatic hydrocarbons containing from five to fourteen carbon atoms and at least one unsaturated aliphatic carboxylic acid having from three to ten carbon atoms, adding an alkali solution to the pulp to convert said carboxylic acid to an alkalimetal salt thereof, and then separating a concentrate rich in the desired mineral values.

2. The process of separating ores by froth flotation which comprises subjecting an aqueous pulp of the ore to froth flotation in the presence of a mixture of saturated and lmsaturated aliphatic straight-chain hydrocarbons having from five to fourteen carbon atoms and at least one alkali metal salt of an unsaturated aliphatic carboxylic acid having from three to ten carbon atoms.

3. The process of froth concentrating ores which comprises adding to an aqueous pulp of the ore a mixture composed of saturated and unsaturated aliphatic straight-chain hydrocarbons containing from five to fourteen carbon atoms and at least one unsaturated aliphatic carboxylic acid having from three toten carbon atoms, converting said aliphatic carboxylic acid to an alkali ANDERSON w. RAISTON. WILLIAM 0. POOL. 

